is medium format dying?

Currently medium format backs go up to 80MPx for a single exposure. As we all know the increase in MPx follows law of diminishing returns and at 10x the cost of d800 MF backs seem like a poor choice for anything other than snobbery of saying "i have most MPX possible". Do you think digital MF is dying? I'd agree that now it is far from dead, it has its niche applications. Lets face it, next high res camera from nikon (d900 or d4x) will probably be close to 50 MPx, so is there really a justification of spending 25K+ for 100MPx medium backs of the future?

I bought d800 because of its built quality; in terms of IQ my d90 was working just fine. So, i'd think it is becoming harder and harder to justify spending $25K-$50K on an MF digital back since IQ is becoming only marginally better.